1. Field of the Invention
The present invention relates to an image forming technique, and more particularly, to an image forming system that includes an information forming apparatus for forming images on recording media, a sheet feeder for supplying recording media to the image forming apparatus, and post-processing apparatuses for performing post-processing to recording media on which images are formed.
2. Description of the Related Art
In recent years, with enhanced speed and image quality of image forming apparatuses that use in electrophotographic method and/or ink-jet printing apparatuses, a system called Print On Demand (POD) that can handle a large number of copies or jobs has emerged.
In POD, a printing operation and its post-processing are conducted in accordance with individual operators' needs in an office environment in which an image forming apparatus is connected to apparatuses capable of bookbinding or cutting as well as a sheet feeder for feeding various types of recording sheets to the image forming apparatus.
In a conventional image forming system for application to POD that is made up of a number of apparatuses such as image forming apparatuses, sheet feeders and post-processing apparatuses, order of connection or arrangement among the apparatuses are defined by dedicated lines connecting the apparatuses. By communicating over the dedicated lines, the apparatuses exchange data relating to printing jobs and process a series of printing jobs including sheet feeding, image formation and post-processing.
When a failure such as paper jam occurs while recording sheets are conveyed among the apparatuses, the only action one can take is to stop the entire image forming system, and in such a case, a large number of recording sheets can remain in the image forming system. To solve this problem, apparatuses have been invented that have a discharge tray to which recording sheets being conveyed are urgently discharged (hereinafter referred to as an “escape tray”).
Also, connection of apparatuses, such as an image forming apparatus and post-processing apparatuses, with dedicated lines fixes the configuration of the image forming system or arrangement of the apparatuses. It thus is difficult to change order of arrangement of apparatuses making up an image forming system or to add a new apparatus in accordance with users' usage (e.g., printing format and post-processing utilized). Consequently, image forming systems that allow flexible change of arrangement have been also proposed.
An example of such prior art is one disclosed in Japanese Patent Laid-Open No. H11-232243.
In a conventional image forming system, however, urgent discharge of recording sheets cannot be carried out unless all apparatuses recognize where in the image forming system an escape tray is positioned.
Especially when one is allowed to flexibly change the order of arrangement among apparatuses, the position of an escape tray will be also changed along with repositioning of apparatuses constituting the image forming system. Conventional image forming systems have the problem of needing to locate an escape tray for all possible combinations corresponding to repositioning of apparatuses, which can complicate control of these image forming systems.